IO4 THE FROG 



Permanent mounts of the spermatozoa of a frog or a 

 salamander may be prepared by fixing the seminal fluid in 

 Zenkers fluid, staining in bulk in Delafield's hsematoxylin, 

 destaining and mounting in the manner prescribed for 

 red blood corpuscles; the material should be counter- 

 stained on the slide with Congo red. In addition the fol- 

 lowing preparation is desirable : Obtain the ripe testis of a 

 urodele (Cryptobranchus or Amphiuma), fix in Telly es- 

 nicky's fluid or Carney's fluid, cut transverse sections about 

 IO/A thick, and stain on the slide with Delafield's haematoxy- 

 lin and Congo red, or with iron hsematoxylin followed by 

 Bordeaux red. Under low power, demonstrate the bundles 

 of nearly ripe spermatozoa, and the immature germ cells 

 (spermatogonia). If properly stained, such a preparation 

 affords a striking and beautiful object. The testis of the 

 frog is not so well suited for this demonstration. 



6. Mitosis. Material favorable for the study of karyo- 

 kinetic figures is furnished by teleost embryos in the early 

 cleavage stages (eight to sixty-four micromeres). Eggs of 

 the whitefish (Coregonus) may be obtained from fish hatch- 

 eries. Fix the material in corrosive acetic for a few minutes, 

 then wash and preserve in formalin. With needles remove 

 the blastoderm, imbed it in paraffin and cut horizontal sec- 

 tions ; stain with iron hsematoxylin and counterstain with 

 Bordeaux red. 



Remarkably large and clear karyokinetic figures may be 

 obtained by cutting horizontal sections of the early cleavage 

 stages of the urodele Cryptobranchus, but the material is 

 not abundant enough to be used extensively for class work. 



Karyokinetic figures are numerous in the epidermis of 

 urodele embryos or larvae, particularly if obtained from the 



